Automobile parts, bicycles, toys, appliances and other industrial and consumer articles are conventionally spray painted in areas called spray booths wherein water curtains are employed to wash the air and to remove over-sprayed paint, lacquer or enamel solids. The wash water is then treated to remove paint solids, and the treated water is recirculated.
A water curtain is typically created by pumping water into a trough above the overspray area. The overflow from the trough is then controlled so that a uniform sheet of water falls along the length of the trough and down the booth's wall. Spray nozzles are also commonly used. Droplets of oversprayed paint, emitted by a spray gun, contact and are captured by the water curtain.
A major problem associated with spraying operations concerns the tacky or adhesive nature of the over-sprayed coating materials. Solids tend to agglomerate and accumulate on the walls, ceiling and floor of the spray area and to clog water spray equipment, recirculating pumps and the like. Thus, the overspray, or paint mist, captured in the water system of a spray booth must be detackified, or "killed", before it adheres to the walls, piping, etc. of the spray booth. Paint that sticks to spray booth surfaces usually cannot be easily removed from the equipment and tends to build up overtime, which hampers spray booth efficacy.
The term "paint killing", as used herein, refers to the act of detackifying oversprayed paint in paint spray booths.
"Paint", as used herein, is a generic term which encompasses all common varieties of water insoluble coatings commonly applied in spraying operations, including but not limited to oil base paints, enamels and lacquers. These products, if untreated, readily adhere to the walls of spray booths and any other surface that they contact, such as the surfaces of water distribution piping, spray nozzles etc.
One solution which has been found to have practical application to the problem involves the use of chemicals which, when added to spray booth water, detackify paint solids. A wide, variety of chemicals have been proposed for this purpose, including compositions containing polymers and multi-valent metal salts which form insoluble hydroxides at pH's greater than about 7. The use of combinations of this type are described in U.S. Patents: U.S. Pat. Nos. 3,861,887 to Forney; 3,990,986 to Gabel et al; 4,002,490 to Michalski et al; 4,130,674 to Roberts et al; and 4,440,647 to Puchalski. While these compositions are generally effective in detackifying and removing paint over-spray, a need exits for water-based, stable alkaline compositions which have high efficiency in order to increase productivity and to achieve a high degree of effectiveness for all types of paints and particularly solvent-borne paints, lacquers and enamels.